Agreement is sign that pro-independence groups are eager to maintain pressure on Spain’s central government

MADRID—Catalonia’s two main separatist parties have agreed to support the re-election of ousted leader Carles Puigdemont as president, in a sign that pro-independence groups are eager to ratchet up the tension with Spain’s central government.

The separatists’ agreement is the first significant step toward forming a new government in the restive Spanish region following regional elections Dec. 21. That vote was called after Spanish Prime Minister Mariano Rajoy imposed direct rule on the region in October in an attempt to quell...